1. Field
Embodiments relate to the placement and movement of sub-units of a storage unit in a tiered storage environment.
2. Background
In a tiered storage environment different categories of data may be assigned to different types of storage media in order to reduce total storage cost. The categories may be based on performance requirements, frequency of use, the volume of data, access density, and other considerations. For example, recently or more frequently accessed data or data that is expected to be used within the next few minutes may be stored on Tier-1 storage such as solid state disks (SSD), where SSDs are relatively expensive per unit of storage but have high performance characteristics. Data that is currently being used or expected to be used within the next few days may be stored on Tier-2 storage that includes less expensive media such as enterprise drives. Data that is unlikely to be used within the next few days may be stored in Tier-3 storage that includes still less expensive media such as nearline drives. Nearline storage (where the word “nearline” is a contraction of near-online) is a term used in computer science to describe an intermediate type of data storage that represents a compromise between online storage (supporting frequent, very rapid access to data) and offline storage/archiving (used for backups or long-term storage, with infrequent access to data). It may be noted that, tiering is not just for data that is expected to be used or not expected to be used within the next few days and it may also be based on access density. For example, if two pieces of data are both used every day (maybe even every hour), but the Input/Output (I/O) per second is very high on one, and very low on the other, then the higher Input/Output per second data may be moved to tier-1 but the lower Input/Output per second data may not be moved.
A storage controller may control storage volumes storage in a tiered storage environment. The storage controller may receive input/output (I/O) commands from a host computing device coupled to the storage controller, and provide access to the data storage in the tiered storage environment to the host computing device.